Bad Customer service

I went to Pick n Pay at San Ridge, Midrand. However today I was left with a bitter taste in my mouth. The treatment I received was really appalling and not handled in a proper manner. I spoke to the lady who was assisting me at the till to let her know that I was over charged because the shelf had priced the black bags for R19.99 and I was charged R26.99. She called one of her colleagues to get the price tag. When Vuyi came back with it she showed me the tag from a distance and expected me to understand the non verbal communication. I then showed her my receipt so she could verify the error. She then spoke to her colleague who had initially sent her for the price tag. The colleague simply said \ I am done with her cause I took payment already